1. Field of the Invention
The present invention concerns a system and a method for purging high purity interfaces. More specifically, the present invention concerns a manifold system and a method for purging interfaces connected to containers of high purity, low vapor pressure chemicals, wherein potential areas of entrapment of the low vapor pressure chemical are eliminated.
2. Description of Related Art
Certain manufacturing processes require the use of low vapor pressure chemicals at high purity levels. One example is semiconductor manufacturing, which requires the distribution of highly reactive, low vapor pressure chemicals in high purity conditions, in order to avoid unwanted contamination during the fabrication process and to maintain competitive process yields. These low vapor pressure chemicals include, among others, organo-metallic precursors such as tetrakis(dimethylamido) titanium (TDMAT), tetrakis(diethylamino) titanium (TDEAT), tantalum pentaethoxide (TAETO), copper hexafluoroacetylacetonate-trimethylvinylsilane (Cu(hfac)TMVS), tetramethyltetracyclosiloxane (TMCTS), tetraethyl ortosilicate (TEOS), and trimethylphosphate (TMP). Typically, these low pressure chemicals are stored in containers having a capacity varying from 100 milliliters to 200 liters, which are known by a variety of common and trade names such as “canisters,” “ampoules,” or “hosts”, and are delivered to chemical vapor deposition (CVD) process tools, either by a direct liquid injection (DLI) process or by a “bubbler” process.
With DLI, the low vapor pressure chemical is delivered to a process tool by injecting a push gas (generally, an inert gas such as nitrogen or helium) through a first manifold into the container, in the headspace above the low vapor pressure chemical in liquid state. The increase in gas pressure inside the container causes the low vapor pressure chemical to be ejected from the container through a diptube immersed in the chemical and then through a second manifold connected to the container, and to be delivered eventually to the process tool, either directly, or by means of an intermediate, “refill” container.
With the “bubbler” process, a push gas (generally, an inert gas such as nitrogen or helium) is injected into the container through a first manifold connected to the container and through a diptube immersed in the low vapor pressure chemical in the container. Instead, the low vapor pressure chemical is supplied to the container as a liquid by means of pressurized gas delivery through a second manifold. The container is heated, in order to increase vapor pressure and to saturate the bubbling gas with vaporized chemical, and the bubbling mixture of gas and chemical is then ejected from the container through a third manifold and delivered to a process tool. The container needs to be refilled with the low vapor pressure chemical on a regular basis. A first container storing liquid low vapor pressure chemical may act as a “refill” container, providing a continuing supply of low vapor pressure chemical to the primary, “bubbler” container.
From time to time, it is necessary to replace and clean a container storing liquid low vapor pressure chemical, for instance, due to maintenance requirements, or due to decomposition of the low vapor chemical within the container, or for other reasons. Before detaching the container from the process chemical delivery lines, the low vapor pressure chemical must be completely removed from the points of connection between the manifold valves and the process lines. Typically, the low vapor pressure chemical is evacuated and purged through a multi-step procedure comprising sequences of blow cycles, which push the residual chemical into the container, and of vacuum cycles, which vaporize and remove the chemical particles trapped into the manifolds. Because of the high level of decontamination required, and because some liquid low vapor pressure chemical may remain trapped within the interstices, or dead spaces, of the system, this procedure is extremely time consuming and affects process yields significantly. Therefore, there is a need for a manifold system that can be purged with reduced cycle times.
Different invention have been disclosed in the prior art addressing the above needs to different degrees. U.S. Pat. No. 5,964,230 and U.S. Pat. No. 6,138,691, both to Voloshin et al., teach a solvent purging system that not only adds complexity to the purging procedure, but that also creates the additional requirement of expensive decontamination of highly toxic chemicals from the solvent.
U.S. Pat. No. 6,431,229 to Birtcher et al. discloses a solventless, purgeable, diaphragm valved manifold for low vapor pressure chemicals, comprising a block valve assembly that includes two diaphragm valves. There remains a dead space between the two valves in the valve block assembly, which complicates cleaning and which requires longer purge cycles in order to remove the chemical from that dead space.
U.S. Pat. No. 6,648,034 to Birtcher et al. teaches a purgeable manifold for low pressure chemical containers, with similar features and drawbacks as the invention taught in U.S. Pat. No. 6,431,229.
U.S. Patent Application 2003/0131885 to Birtcher et al. discloses a cabinet for chemical delivery with solvent purging, which includes some of the features and drawbacks of the inventions disclosed in U.S. Pat. Nos. 6,138,691 and 6,431,229.
Japanese Patent JP 2004-063833 A to Yoshitome Koichi teaches a low pressure chemical supply system for use in a CVD process, comprising a manifold block fed by entry and exit valves and containing a bypass route with two additional valves. While this invention appears to offer process improvements over the invention disclosed in U.S. Pat. No. 6,431,229, this supply system still contains dead spaces where the low pressure chemical may be trapped, requiring extended purge cycles.
None of the above inventions appears to disclose a system or method for purging high purity interfaces that eliminates dead spaces and also costly specialty valves.